It is proposed that a Philips CM12 transmission electron microscope and an Optronics C-4100SP microdensitometer be purchased. These instruments are necessary for structural studies by members of the research groups of Drs. Flicker, Fleischer, Robinson, Stubbs, LeStourgeon, and Williams. Dr. Flicker is examining the structure of actin and myosin. She plans to utilize cryo-electron microscopy to visualize different conformational states of actomyosin and localize functionally significant sites on the proteins. Dr. Robinson has developed a procedure for preparing two-dimensional crystals of neurotoxins, well suited for examination using electron microscopic techniques. Dr. Fleischer works on channels involved in excitation-contraction coupling in muscle. His goal is to examine the structures of the channels in open and closed states using cryo-electron microscopy. To date, Drs. Robinson and Fleischer have had to depend on external collaborations to obtain data for electron microscopy and image processing. Dr. Stubbs is determining molecular structure of helical plant viruses, Dr. LeStourgeon is concerned with the structure of nuclear ribonucleoprotein particles, and Dr. Williams studies microtubules and microtubule-associated proteins. Studies of all of these protein and nucleic acid assemblies would benefit from the relatively high resolution and state of preservation available through cryo-electron microscopy.